ISRO | ISRO CS 2020 | Question 8
In a 8-bit ripple carry adder using identical full adders, each full adder takes 34 ns for computing sum. If the time taken for 8-bit addition is 90 ns, find time taken by each full adder to find carry.
(A) 6 ns
(B) 7 ns
(C) 10 ns
(D) 8 ns
n = 8 Ripple Carry Adder SUM delay from each Full Adder Sdelay = 34 ns CARRY delay from each Full Adder Cdelay = ? Overall delay = T = 90 ns
T = Sdelay + (n – 1)Cdelay 90 = 34 + 7 × Cdelay Cdelay = 8 ns
So, option (D) is correct.
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